This invention relates generally to electrical grounding systems, and more particularly concerns a system of grounding receptacles which are linked by a common ground wire and grounded to a common point.
Electrical service is provided in maintenance facilities such as submarine berths, shipyards, automobile repair garages, computer repair benches, and the like, in order to power tools, computers and the electrical equipment required for maintenance and repair. In order to ensure adequate safety and performance of the electrical equipment, it is necessary that the electrical equipment be grounded in some fashion. Conventionally, metallic receptacles have a copper rod threaded into the bottom, and the receptacles are embedded in a concrete pad adjacent a submarine berth, bench, bay, or the like, with the copper rod extending into the earth or concrete below. The electrical equipment is connected to the ground by a wire having a matable clamp, which is connected to the grounding receptacle terminal. In a normal installation, there may be a large number of electrical connections along with a large number of metallic ground receptacles.
Each metallic receptacle itself acts as a groundinng device and subjects the equipment connected to it to the ground potential of the earth in which it is situated. Even if the individual electrodes are somehow linked together to attempt to eliminate grounding voltage potential differences, each grounding receptacle may contribute a certain amount of in-ground variation potential depending on where it is placed. This is often caused by variable soil conditions, such as moisture content, electrolyte composition, metals content and the like. When measurements are taken of the electrical grounding system and the ground point on each receptacle, it is found that some receptacles provide a better ground to earth than others do. A voltage potential can be created between two or more pieces of electrical equipment which can affect the performance of equipment such as computeers that, although attached to separate grounding receptacles, are in communication with each other over some sort of transmission line. Data signal levels can be transmitted inaccurately if there is an extraneous current passing between the transmitting and receiving devices. Moreover, if the voltage potential is large enough, terminal inputs or ports can be destroyed. If the equipment has protective transistors installed internally, these can be burned out by inconsistent or different voltage levels where zero potential difference is expected.
Where electrical equipment aboard a seagoing vessel, such as a submarine, is to be grounded to the earth, an additional problem exists. The vessel can act as an electrode and the earth acts as a second electrode. Sea water, which contains electrolytes, may be present in the earth near the sea water and a current may be created across the gap between the vessel and the earth. In this situation, the ground potential could be affected, causing inaccurate measurements of ground potential. Additionally, the equipment acting as the electrodes, such as a cabinet, frame or chassis, may corrode faster because of the oxidation of one of the electrodes where a current is created. This can also occur where the atmosphere acts as the electrolyte, such as in the vicinity of sea water.
There is a need, then, for a system which can electrically ground a number of pieces of electrical equipment so that the variation in ground potential is reduced. Such a system should enable each piece of equipment to be grounded so as to share the same ground wire, thus virtually eliminating any difference between individual ground potentials.